Development of the kidney begins when the ureteric bud induces the metanephric mesenchyme to differentiate into epithelial cells which then undergo a complex transformation to form the glomerulus and tubule. we found that this mesenchyme is composed of stem cells whose progeny can populate all nephron segments. The fate of the induced cell becomes restricted after induction in that they can now generate only cells for a single segment of the nephron. To identify the molecules that are involved in this restriction of fate we will generate monoclonal antibodies against early nephrogenic structures such as renal vesicle and S-shaped bodies. Antibodies that are lineage-specific or stage-specific will be identified and studied for their effect on tubulogenesis in vitro suing an organ culture. The antigens identified by these functionally inhibitory antibodies will be cloned from an expression library which has already been constructed. We have also generated immortalized mesenchymal cell lines and will also immortalize ureteric bud cells. Using two cell lines in co-culture we will identify the molecules that are involved in the initial process of induction. The effect of three dimensional matrices will be tested as will the role of membrane contact between the two cell types. This in vitro assay system will also allow the detection and identification of soluble factors produced by one cell type that acts as mitogens or chemoattractants for the other cell type.